Can an abdominal ct scan w/contrast show ibs?

No: There is no specific pathology that can be identified by CT scan in IBS.

Not really!: The CT will show spasm or edema ( swelling of the bowel wall) but you need something such as endoscopic studies to rule out any inflammatory disease which is a serious health issue, unlike that of irritable bowel which is also painful but does not progress in most cases.